As he says, "Many hoteliers assume that only backpackers or very budget-conscious consumers will consider using these sites, but they would be incorrect. In fact, AirBnB lists and secures bookings for many luxury properties including apartments, villas, mansions and castles (there are currently 600+ listed on the site), private islands and, in 2011, even the entire principality of Liechtenstein!"

Could your headquarters hotel lose your block's room nights to people booking around the block to crash at a local apartment? I think it's a distinct possibility. Airbnb more than doubled its listings in 2013 to 300,000 worldwide, served more than 4 million guests, and is in line to become the world's largest hotelier in 2014, overtaking even the likes of InterContinental Hotels Group and Hilton Worldwide.

And while conference-goers aren't likely to be looking to stay in a treehouse or a yurt, an apartment around the block where an entire group can stay at a reasonable cost could be a contender. I think the time is ripe for planners to add Airbnb and similar sites to the list of things like room block pirates and online booking sites that could potentially become a part of the attrition problem. And hoteliers, I'd heed Mourier's call to monitor rates from these sites, enhance services and make stays more personalized, and use the best tools you can find to manage your data collection, analysis, and pricing.